Partial Flow Dilution System with Double Dilution for PM Sampling under Transient Test-Cycles

Automobile Particulate Matter (PM) Emission regulation requires gravimetric determination of PM collected on filter media under simulated driving conditions in the laboratory traditionally in a full flow Constant Volume Sampling (CVS) dilution tunnel. There have been discussions about whether current sampling and measurement practices are sufficiently accurate in quantifying PM at the upcoming 1mg/mi PM emissions standards of CARB LEV III. Sampling technique alternative to a CVS such as a Partial Flow Dilution (PFD) system has already been developed and is acceptable for certification testing. Lower dilution ratios and higher filter face velocity (FFV) are options to load traceable amount of PM on filter in case of light duty vehicle (LDV) testing. On the other hand higher dilution ratios and lower FFV are required for heavy duty engine (HDE) testing to keep the PM loaded on filter <400μg. A PFDS with a single dilution tunnel cannot support both LDV and HDE testing where a wide range of FFV and dilution ratios are required.

A new PFD system with double dilution has been developed in this study to meet PM measurement requirements of LDV and HDE transient testing. Two identical dilution tunnel configurations are employed for 1^st stage and 2^nd stage dilution. It uses fast response venturi flow meters that are free from errors caused by differences in the physical gas densities, or thermal capacity variations. The system can give minimum dilution ratio of 5:1 to maximum of 2500:1 and can operate under different control modes for dilution; proportional sampling mode and fixed dilution ratio mode. The PFD system developed in this study meets the sampling requirements of transient test cycles both for LDV and HDE with good flow accuracy, dilution ratio accuracy, and fast transient response for proportional sampling.